Antibodies reacting with human ovarian cancer cells have been coupled to Pseudomonas toxin. Such immunotoxins kill ovarian cells in tissue culture and human ovarian cancer cells growing in the peritoneal cavity of nude mice. A number of monoclonal antibodies reacting with human ovarian cancer cells have been isolated by the hybridoma technique. Phase I studies have been begun to treat adult T-cell leuklemia with an antibody to the Il2 receptor conjugated to Pseudomonas exotoxin.